Phase plane correlation (PPC) is an efficient technique for correlating two images, resulting in a correlation surface in which the peaks and their respective amplitudes are a direct indication of the similarity in image luminance between the two images. In the PPC technique, a normalization step attenuates dissimilarities in luminance that results in a normalized correlation surface that is far more discerning than simple correlation.
There are historical reasons for performing a luminance only analysis, such as PPC. PPC originated out of a need to perform image registration for mapping purposes. The PPC technique is an ideal tool for computing, in a very efficient manner, the translational displacement between two images when it was assumed that the images differed only by translation and variations in luminance. However, when complex motions become part of the image scene, the interpretation of the PPC surface becomes much more complicated.
The traditional PPC technique only takes into account the luminance of the images. As a consequence of this, if two portions of an image are similar in luminance, then their respective correlation will be strong; even if the pixels are part of different structures in the image. This is a fundamental limitation to applying a PPC technique strictly to luminance.
Therefore, there exists a need for an improved method and apparatus for image processing and correlation that takes into account image structure.